Heat treatment of gear teeth



1944. F. s. D'ENNEEN ETAL 2,356,150-

HEAT TREATMENT OF GEAR TEETH Filed April 25, 1941 2 Sheets-Sheet 1 F g a :ZI VENTORS.

m Km Patented Aug. 1944 HEAT TBEATMZ ENTOF GEAR TEETH Francis S. Denneen, Cleveland, and William C. Dunn, Shaker Heights, Ohio; assignors to The Ohio Crankshaft Company, cleveland ohioya corporation of Ohio Application April 23, 1941, Serial No. 389,847

2 Claims.

The present application as a continuation in part of our co-pending application, Serial No. 174,810, filed November 15, 1937, is directed to apparatus and method for the heat treatment of projections on the'surfaces of articles, particularly projections such as gear teeth on metallic articles.

The invention herein disclosed is particularly well adapted to the heat treatment'of projections which extend for some distances along thesurface of the article such as the teeth of gears having wide faces. With our apparatus and method it is In general, the object of the invention has been v to provide a method and apparatus for hardening internal or external projections on a member of the class mentioned above.

A further object of this invention has been to provide a gear or other article of the general character of a gear having hard surface zones to resist wear on contacting surfaces. Another object has been to provide a metal tooth'or rib having a tough and ductile core and root section adapted to resist heavy bending or other stresses caused by shock or impact in the section in which such high stresses occur. An additional object has been to provide a tooth having a hard surface "zone so bonded to the core or underlying metal A still as to resist cleavage of this hard zone. lurther object has been to provide a method of procedure in the formation of such hard surface zone on a tooth previously formed and heat treatrequire a high degree of skill for its operation.

invention to the various objects heretofore outlined.

When it is necessary to harden large areas, frequently the power available is not suflicient to heat all the desired parts of that area simultaneously. Therefore this area must be heated in sections. Small parts may be hardened progressively bycausing the inductor to pass over the area from One portion to the other and quenching back'of the inductor as fast as the inductor advances past part of the area heated. Alternatively, teeth or other projections of small or intermediate size may be heated and quenched without relative movement of the inductor and the teeth or projections and surface zones of several such teeth or projections can readily be hardened simultaneously. V

The manner in which we accomplish our invention is illustrated -by the following description and the appended drawings. The novel features of the invention are summarized in the claims.

In said annexed drawings: a i Fig. 1 illustrates the general arrangement and form of an inductor for heat treating surfaces of three projections simultaneously taken as indicated at i-i of Fig.2.

Fig. 2 is a section substantially at 2-2 of Fig.1. Fig. 3 shows a modification of the apparatus of Fig. 1 taken substantially at 3-4 of Fig. 4 and which is adapted to heat treat the surfaces of four projections simultaneously.

Numerous other objects will become apparent and drawings relate to gears we do not confine ourselves tohardening gears alone but apply the Fig. 4 is a section substantially at #4 of Fig. 3. In Figs. 1 and 2 the inductor comprises conductors 36 and 31 joined at their outer ends as at 38 to form a loop, the loop lying substantially tangentially to the pitch line of the teeth. Current of suitable frequency is supplied by the transformer 39. The conductors are inserted intooth tooth spaces are usualbut this arrangement spaces of the gear 40. The lyadjacent spaces as shown, is not necessary since two or more teeth may intervene between the two spaces occupied by the conductors.

The location of a conductor is determined to a large extent by the frequency employed and the number of tooth surfaces it is desired to harden at one time. When the inductor is arranged substantially as shown in Fig. 4 and current or moderatefrequencies such as 1000 to 2000 cycles per see. is employed the sides of tooth 4| are heated with a relatively'small amount of. heating in the sides'of teeth 42 and it, these being outside of the loop.- The heating effect inthe teeth is increased by reducing the spaces between the teeth and the inductor members" and 31; When the frequency is materially increased, for instance to the order of 100,000 cycles, per sec., effective heating current will be generated in the adjacent surface zones of teeth 42 and 43 outside of the loop as well as in the surface zones of tooth 4| adjacent to the conductor members within the loop,

'I'o equalize heating in the several teeth, the spacing is changed to correspond with the frequency. As the frequencies become lower, the space between the tooth 4| Within the loop, and the conductor, such as 31, becomes greater and the space between the tooth outside ofthe loop, such as 43, and the conductor 31 .becomes less. At extremely high frequencies the spaces are nearly equal with the conductors enlarged to lie close to the surfaces of both teeth. The face of the conductor adjacent to the tooth surface is frequently formed to vary in distance from this surface so as to control the distribution of the heating, the least distance usually being at the top of the tooth. The conductors are usually hollow to provide passages for cooling water. Quenching is accomplished by conduits such as 44 and 45 which usually lie parallel with the tops of the teeth and which have outlet passages such as 46 disposed to direct the quenching fluid into the spaces between the conductors and the faces of the teeth, the flow being under pressure and sweeping over the surfaces of the teeth vigorously enough to remove bubbles of steam or other vapor forming on these surfaces during quenching.

To prevent the inductor members 36 and 31 I from interfering with a free flow of the quenching fluid it is often desirable to remove the inductor during quenching. To accomplish this,

the inductor is hinged as at 41 which permits the heated faces of the teeth, the fluid entering the spaces between the teeth and the conductors. As in Figs. 4 and 5, the spacing between the inductor members and the teeth within the loops is greater than the spacing between these inductor members and the teeth outside the loops when current of ordinary high frequency is employed. Thus, the spaces at '58 are greater than spaces at 59 when such current is used. On the other hand, when high frequencies are used the spaces at 58 become relatively smaller and become substantially equal to the spaces at 59 when extremely high frequencies are employed which is 'required to obtain substantially equal heating in all the tooth faces.

It will be understood that projections of varithe surface zones of the projections.

the inductor is moved away from the gear far enough to permit rotating the gear on its axis. The gear is then rotated by a suitable mechanism and indexed to hold another unhardened tooth or group of teeth in heating position. The inductor members are then brought back into the spaces between the teeth of the unhardened group.

When a more rapid rate of hardening is desired and suflicient current of high frequency is available an inductor of the form shown in Figs. 3 and 4 is employed. This inductor is composed of a central conductor and two lateral conductors 5| and 52, the latter usually being smaller than conductor 50. Conductor 50 passes between two teeth such as 53 and 54 and supplies current for the conductors 5| and 52 which together serve as a return circuit. These latter conductors are located in tooth spaces adjacent to teeth 53 and 54 on the sides of these teeth opposite to the space occupied by conductor'50 and are in heating relation with teeth 53 and 54. The conductors are usually hollow to provide passages for fluid ordinarily serving for both cooling the inductor and quenching the teeth. Other conduits for additional quenching fluid, such as 55 and 56, are frequently employed and have outlet passages 51 arranged to project this quenching fluid under pressure against and along the Other modes of applying the principle of our invention may be employed instead of the one explained, change being made as regards the structure herein disclosed, provided the means stated by any of the following claims or the equivalent of such stated means be employed.

We therefore particularly point out and distinctly claim as our invention:

1. In apparatus for hardening surface zones of projectionson a metallic article, the projections being spaced along a base surface of the article and extending outwardly from said base surface, a U-shaped conductor having substantially parallel opposite sides, each of the sides having a face adapted to be brought into substantially parallel relation with a surface zone of a projection, means for supplying periodically varying current to the conductor to induce heating current in the said surface zones, means moveably supportin the conductor at an end of a sideof the conductor, means for guiding the conductor into a preselected position relative to a projection of the article when the conductor is moved toward the base surface of the article to bring a face of the conductor into spaced relationwith a surface zone of the projection, and means for deliveries quenching fluid to the surface zones of the projections, the quenching means comprising a quenching member disposed to lie substantially opposite an outer end of the aforesaid projection, the said quenching member having discharge passages directed toward a space adapted to be occupied by the projection of the article, the quenching member being of less width than the space between the conductor members to pass between the said members when the conductor is moved on its support.

2. In apparatus for simultaneously hardening four surface zones of projections on a metallic article, the projections being spaced along a base surface of the article and extending outwardly from said base surface, a U-shaped conductor having substantially parallel opposite sides, each of the side having opposite faces adapted to be brought into substantially parallel relation with surface zones of adjacent projections when the side is inserted between the adjacent projections, means for supplyin periodically varying current to the conductor to simultaneouslyinduce heating current in the four surface zones lying adjacent to the sides of the conductor, means moveably supporting the conductor at an end of a side of the conductor, said supporting means comprising means for guiding the conductor into a preselected positionrelative to the projections of the article when the conductor is moved toward the base surface of the article to bring faces of the conductor into spaced relation with cor-- responding surface zones of the projections, and

means for delivering quenching fluid to the surface zones of the projections, the quenching means comprising spaced quenching members FRANCIS S. DENNEEN. WILLIAM C. DUNN. 

